Polymeric materials are continually being sought which have a special affinity for selected chemical entities either for the purpose of separation of desirable products, such as aldehydes from a reaction mixture, or for removal of unwanted or harmful entities (such as (heavy) metal cations, related anions, nitrites, or chlorine compounds) from such mixtures or from water in the environment. It is desirable that such polymeric materials have high specificity for the chemical entity or entities in question, that they be easily removed from the solution when they have captured the chemical entity in question, and that they be relatively easy to strip of the entity and be regenerated for further use.
For example, isolation of the products from reaction mixtures is one of the most important steps of chemical processes. Polymer-supported extracting agents offer simplicity for isolation of one of the products from these reaction mixtures. Crosslinked polymers are often preferred as support, due to their insolubility. In such a case, isolation of one of the entities is reduced to a simple filtration. If the functional group attached to the crosslinked polymer is selective for a compound targeted, it will be possible to pick it up and separate it easily from the mixture.
In particular, ideal polymeric separating agents for nitrites, organic chlorine compounds, metal ions including readioactive metal ions, counteranions of metal salts and aliphatic and aromatic aldehydes would be highly desirable, and are presently being sought.
In some respects, polymeric protecting agents may also be considered as trapping agents. However, for the case of "protecting", the aim is to protect any functional group of a compound for the next reaction. But in the trapping, a polymeric reagent binds selectively to one of the components of a reaction mixture. This phenomena has been termed a "Fishing out process" [1]. In the literature, there appear many reports on the use of polymeric protecting agents for alcohols [2], aldehydes [3] and carboxylic acids [4]. But, fewer reports appear about polymeric trapping agents. Polymer-supported semicarbazide has been demonstrated to be efficient for removal of small quantities of aldehydes by means involving hydrazide groups [5]. But the regeneration of this polymeric extracting agent is not possible due to the hydrolyzable hydrazide groups and the reagent described is not appropriate for recycling.
Crosslinked polymers bearing various ligating groups are promising materials for hydrometallurgical applications, water purifications etc. Recent attempts have been made to incorporate many different chelating groups into polymeric networks [13, 14]. Although many chelating polymers with high metal-uptake ability have been reported, these materials suffer from hydrolytic instabilities. In view of this, polymers having hydrolyzable or oxidizable groups are not suitable for large scale applications, even though they have good metal-sorption abilities.
The present applicant has demonstrated that all-amine ligating polymers offer advantages of non-hydrolysability, better ability of metal sorption and anion-binding ability. Because in these polymers chelation is expected to occur by formation of cationic metal complexes, the counter-anion of metal salts must also bound-ionically either to the cationic complex being formed, or to the free other amine groups of the polymer. Coordination chemistry of low-molecular-weight amines such as ethylene diamine [16], diethylene triamine [15] have been well-studied in the literature. With these ligands, the counter-anion of the metal complexes formed is hydroxide or the anion of the metal salt involved. Up to the present, few non-hydrolyzable polyamines are known in the literature. These are polyvinyl pyridines, polyethyleneimine, and polyvinylamine. Among these only polyvinyl pyridines and its monomers are commercially available. Polyethyleneimine is obtained either by cationic ring opening of ethylene imine monomer [16] or by hydrolysis of oxazoline polymers [17]. Whereas vinylamine monomer does not exist, its polymer is prepared by hydrolysis of poly(N-vinyl amides) [18, 19] or poly(N-vinyl t-butyl carbamate) [20]. Recently, the applicant has demonstrated that the polymer can also be prepared by Hofmann's N-bromamide method, from polyacrylamide in ethylene glycol [21]. there appear many papers dealing with metal complexes of poly(vinyl pyridines), poly(vinyl amine) and poly(ethyleneimine) in the literature.
Other available amine-containing polymers which have affinity for metal cations (U.S. patents--Moriya et al.: U.S. Pat. Nos. 4,670,160 and 4,670,180) are hampered by excessive water solubility, which makes extraction difficult and sometimes requires separate coagulants (e.g. FeCl.sub.2, sodium sulfide, etc), or by unacceptable odor due to incorporation of primary amines or evolution of H.sub.2 S.
Nitrite ion is one of the most hazardous chemicals which may present in environmental water. Its acid form (nitrous acid) is very reactive towards many organic compounds such as amines, phenols, alcohols etc. Many reactions involving nitrous acid proceed via a free-radical mechanism and these reactions are rapid. With nitrous acid, phenols give ortho- or para-hydroximino derivatives. Alcohols give nitrite esters. Primary amides readily decompose to give carboxylic acid and nitrogen. This approach has been demonstrated to be useful in controlling conversion of polyacrylamide into acrylic acid [28]. Aliphatic primary amines yield an unstable diazo compound which immediately decomposes into alcohol and nitrogen. This reaction is the basis of the Van-Slyke method which is used for the determination of amino acids [29].
Secondary amines or amides yield nitrosamines or nitrosamides respectively. Both products are well-known carcinogenic compounds. Since peptide linkages are secondary amides, nitrous acid is also a very harmful chemical for living organisms.
Furthermore, from an environmental point of view, pollution of water sources arising from nitrite ion is gaining increasing importance, due to extensive exploitation of nitrogen-containing fertilizers. Hence nitrite-removal is a major problem to be solved. An effective special sorbent for the removal of nitrite ions would constitute an important advance in the art.
Moreover, exploration of some compounds for the above uses has been hampered by the danger of unstable and highly exothermic reactions, especially in connection with resins made by combining polyethylene polyamines with epihalohydrins.
The above problems are resolved in a novel and unobvious manner by the present invention.
It is therefore a primary object of the present invention to provide a highly effective polymeric extracting agent for separations and purifications.
More specifically the object of the invention is to provide an agent for effective extraction of nitrite ions, aldehydes, chlorine compounds, metal cations including radioactive ions, (and associated counter-ions), and other chemical entities, even when starting with very low concentrations.
A further object is to provide such a polymeric agent that is insoluble in water or the solvent of the solution in question, so that extraction can be effected by simple filtration without need for separate coagulants.
Another object of the invention is to provide a polyamine polythioagent with no objectionable odor in use.
A still further object is to provide an agent which can be regenerated without acid hydrolysis or other destructive reaction.
Another object of the invention is to provide a method of synthesizing polymers by epoxy ring opening, without the dangers of unstable reaction experienced with the prior art.
Another object is to provide a method of purifying polluted environmental water sources.
These objects and other objects are achieved by the present invention, as taught to those skilled in the art by the present specification and as claimed below.